1. Field of the Invention
This invention relates to a process for the production of alkyl and/or alkenyl oligoglycosides in which a combination of a stirred tank reactor and a falling-film evaporator is used.
2. State of Related Art
Alkyl oligoglycosides, more particularly alkyl oligoglucosides, are nonionic surfactants which are acquiring increasing significance by virtue of their excellent detergent properties and their high ecotoxicological compatibility. The production and use of these compounds have been described just recently in a number of synoptic articles, of which the articles by H. Hensen in Skin Care Forum, 1, (October 1992), D. Balzer and N. Ripke in Seifen-ole-Fette-Wachse 118, 894 (1992) and B. Brancq in Seifen-ole-Fette-Wachse 118, 905 (1992) are cited as representative.
They are normally produced by acetalization of glucose with fatty alcohols in the presence of acidic catalysts. The catalyst is then neutralized, excess fatty alcohol is removed and, if desired, the product is bleached.
There are numerous known processes for their production which are characterized by the use of certain units. For example, DE-A1 4 231 833 (Huls) describes an acetalization reaction which is carried out as a liquid/liquid reaction in a thin-layer evaporator. Another process for the production of alkyl glucosides, in which the acetalization reaction is carried out in an evaporator at an acid value of 1 to 10, is known from EP-A1 0 501 032 (Huls). Finally, a process in which aqueous starch sirup is introduced into the reaction solution through an in-line mixer is known from WO 93/11143 (Henkel).
The discontinuous acetalization reaction is normally carried out in stirred reactors which are equipped with a distillation head for removing the water of condensation. Under laboratory conditions, substantially complete conversions can be obtained in short times, in addition to which the reaction products are distinguished by a low polysugar content. However, scaling-up for industrial application involves difficulties. More particularly, it has been found that much longer reaction times are required for complete reaction of the glucose, resulting in an unwanted increase in secondary products, more particularly the polysugar content, quite apart from longer reactor possession times.
Accordingly, the problem addressed by the present invention was to provide an improved process for the production of alkyl glucosides which would be free from the disadvantages mentioned above.